The question is as follows:
And the answer is E.
I calculated the following:
$\Delta^2f(1) = -6, f(2) = 3, f(3)=1, \Delta f(3)=4.$
Then I stopped and don`t know how to complete because the formula for calculating $\Delta^2f(3)$ contain $\Delta f(4)$. So what shall I do could anyone help me please?